Variable resistor or potentiometer construction



Jan. 22, 1957 L. M. BURGESS 2,778,906

VARIABLE RESISTOR OR POTENTIOMETER CONSTRUCTION Filed July 9, 1953 2Sheets-Sheet 1 Jan. 22, 1957 L. M. BURGESS 2,778,906

VARIABLE RESISTOR OR POTENTIOMETER CONSTRUCTION Filed July 9, 1953 2Sheets-Sheet 2 fi-5. a; 22 :1

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(Z ffaz/wgeg United States Patent VARIABLE RESISTOR OR POTENTIOMETERCGNSTRUCTION Lauren M. Burgess, Lexington, M'ass., assignor, by mesneassignments, to ActonLaboratories, Iuc., Acton, Mass.

Application July 9, 1953, Serial No. 367,028

2 Claims. (Cl. 201-48) The present invention relates to a variableresistor or potentiometer construction, and. more particularly to suchconstruction suited for relatively small and economically manufactureddevices.

The increased use of servo-mechanisms, computer apparatus, and the likehas emphasized the need for relatively small compact variable resistorsor otentiometers. In spite of the fact that such potentiometers have acase, which is only /8 of an inch in diameter or less, the accuracyobtained is surprisingly high, and hence the tolerances permitted inmeeting the specifications of these devices are relatively small. Ingeneral, however, such tolerance specifications have a tendency toincrease manufacturing costs. Accordingly it would be desirable toprovide improved types of construction which will enable the manufactureof relatively small, compact, inexpensive, and yet reasonably accuratevariable resistor devices or potentiometers.

it, therefore, is an object of the present invention to provide animproved compact precision potentiometer construction which is simpleand economical to manufacture.

Still another object of the invention is to provide an improvedprecision potentiometer construction having wiper and contact armstructures which are easy to assemble.

Other and further objects of the present invention subsequently willbecome apparent by reference to the following description taken inconjunction with the accompanying drawings wherein:

Figure 1 is a longitudinal cross-sectional view of a variable resistoror potentiometer constructed in accordance with the present invention;

Figure 2 is a rear view of the device shown in Figure 1 with the rearcover removed;

Figure 3 is a front view of the device shown in Figure 1;

Figure 4 is a longitudinal cross-sectional view of another embodiment ofa variable resistor or potentiometer;

Figure 5 is a rear view of the resistor shown in Figure 3 with the coverremoved; and

Figure 6 is a rear view of the device shown in Figure 4.

Referring to Figures 1, 2 and 3 there is shown a variable resistor orpotentiometer constructed in accordance with the teaching of the presentinvention, and having a cylindrical casing or housing 11 provided at therear with a cover 12. Within the housing 11 there is provided a coaxialboss 13 which carries a metal bearing member 14 having a threadedportion 15. The threaded portion 15 is adapted to be engaged by asuitable fastening nut so that a one hole mounting is provided for thevariable resistor or potentiometer. To preclude rotation of the member14 in the hole, the front side of the casing 11 is provided with aprotuberance or button 16 arranged to fit into a recess or hole in thesupporting bracket or mounting panel for the potentiometer.

The bearing member 14 carries a shaft 17 having a groove 18 into whichis fitted a snap'ring 19 adjacent the forward end of the bearing member14. The inner end of the shaft 17 is provided witha knurled portion 21separated from the rest of thev shaft by an annular recess 22. Theannular recess 22: and. the knurled portion 21 are embedded in a moldedwiper arm support 23. A suitable spacing. washer 24 is interposedbetween the arm 23 and the inner end of. the boss 13. The arm 2'3v atits outer end is provided with a stud 25 of suitable configuration forreceiving a contact arm and slip ring contacts.

The inner end of the boss: 13 is provided with a slip ring 26 connectedby a conductor 27 to a soldering post or connector 28 extending throughthe lower portion of the cylindrical wall of the casing 11. A. pluralityv of similar posts 29 are provided in the cylindrical wall. 11forconnection to the resistance. wire 31 of a resistance element woundon a supporting card 32, which is fitted within: the cylindrical wall 11and insulated therefrom by a suitable sheet of insulating material 33.It will: be noted that depending from the boss 13 is a radiallyextending fin or projection 34 which is to serve as a stop for themotion of the contact arm support 23 and the electrical contacts carriedthereby.

Referring particularly to Figures 1 and 2 it will be observed that thestud 25 of the supporting arm 23 is engaged by a unitary metal structurehaving a flat portion 35 provided with an aperture having on oppositesides of the stud friction engaging spring members 36. From Figure 1 itwill be noted that the front end of the flat member 35 extends inwardlya distance sutficiently so that it will engage the fin 34 when the shaft17 is rotated 180 from the position shown. The inner end of the member35 carries two depending arms 37, each provided with precious metalcontacts 38 which engage the slip ring 26. As may be seen from Figure 2a portion of the fiat member 37 is bent at an angle to form a member 39having a curved contact portion 41 which engages the resistance wire ofthe resistance element.

Figures 4, 5 and 6 show another construction wherein most of the partsare similar to the parts shown in Figures 1, 2 and 3, hence they havebeen given similar reference characters. The principal differencebetween Figures 1 and 4 is the cover construction and the constructionof the unitary contact member which serves as a contact arm against theresistance element and the cooperating contacts, which otherwise wouldengage a slip ring. Mounted on the free end of the arm 23 is a unitarystructure of metal having a flat portion provided with a suitableaperture for fitting about the stud 25 and having spring frictionengaging and retaining lock members 136. The flat portion of the member135 extends toward the front of the casing 11 a distance sufiicient toengage the fin 34 so as to stop the motion of the arm 23. One endportion of the member 135 is reversely bent as at 139, and terminates ina curved contact portion 141. The flat member 135 toward the rear of thecasing 11 is provided with two depending arms 137, each terminating inprecious metal contacts 138. The members 138 engage a contact plate 126which is connected to a soldering post 128. Suitably mounted on the rearcover 12 are additional contact plates 129 which are connected to theends of the resistance wire 31 of the resistance element.

From the foregoing embodiments shown in the drawings it will be notedthat the present construction is extremely simple having a minimumnumber of parts requiring a minimum of machining and assembly work. Itis comparatively simple to assemble the shaft 17 into position and tohold it thereby the retaining lock spring 19. The very simple snap inoperation will either put into position the wiper arm and slip ringcontacts shown in Figure 1 or the corresponding apparatus shown inFigure 4.

While for the purpose of illustrating and describing the presentinvention certain preferred embodiments have been shown in the drawings,it is to be understood that the invention is not to be limited therebysince such modifications are contemplated as may be commensurate withthe spirit and scope of the invention set forth in the accompanyingclaims.

I claim as my invention:

1. The combination in a precision variable resistor or potentiometerhaving a cylindrical casing provided with a resistance element, saidcasing having an end wall carrying a shaft, a cover for said casing,said cover carrying a flat metal plate and a plurality of electricalterminals for said plate and said resistance element, an insulated armfixed to the inner end of said shaft, said arm at its outer end having astud, and a unitary contact structure having an opening and cooperatinglugs to frictionally engage said stud to hold said structure inposition, said structure having a member carrying a contact for engagingthe resistance element and a plurality of members carrying contacts forengaging the plate on said cover.

2. The combination in a precision variable resistor or potentiometerhaving a cylindrical casing provided with a resistance element adjacentthe inner cylindrical wall, said casing having an end wall provided witha boss, a shaft carried by said boss, an arm of insulating materialmolded on to the inner end of said shaft, said arm at its outer endhaving a radially projecting stud, a continuous metal surface carried bysaid casing and connected to a terminal mounted on said casing, aplurality of terminals mounted on said casing connected to saidresistance element, and a unitary contact structure for engaging saidresistance element and said continuous metal surface, said contactstructure having an opening and adjacent locking lugs to receive thestud of said arm to frictionally lock said structure in position on saidarm, said structure having a resilient arm carrying a contact forengaging said resistance element, and a plurality of resilient memberseach carrying a contact for engaging said continuous metal surface.

Schellenger Oct. 24, 1939 Searles et al. Dec. 23, 1952 man...

